Electrical gaseous discharge device



Nov. 14, 1939. c. G. SMITH 2.179.673

ELECTRICAL GASEOUS DISCHARGE DEVICE Filed Nov. 3, 1936 2 Sheets-Sheet 1 25' i lllll Ill ,171 veflior CHARLES 63 5mm Patented Nov. 14, 1939 UNITED STATES PATENT OFFICE ELECTRICAL GASEOUS DISCHARGE DEVICE Application November 3, 1936, Serial No. 108,953 9 Claims. (Cl. 250--27) This invention relates to an electrical gaseous discharge device, and more particularly to such a device which is adapted to rapidly and periodically interrupt the current flow in a circuit.

An object of this invention is to produce such a device which is capable of converting direct current of relatively large current and voltage into alternating current.

Another object of this invention is to produce such a device which utilizes a novel barrier mechanism between a cathode and anode to interrupt the current.

A further object is to devise a simple and effective arrangement for actuating said barrier mechanism.

The foregoing and other objects of this invention will. be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings,

:1)- wherein:

' Fig. 1 is a view partly in section showing one form of the device together with a circuit in which it may be used;

Fig. 2 is a section taken along line 22 of Fig. 3 is a view similar to Fig. 1 showing another modification of this invention; and

Fig. 4 is a section taken along line 44 of Fig. 3.

: The present device is a gaseous discharge tube having a thermionic (or other suitable type of cathode) and an anode; and interposed between said electrodes is a variable barrier to current fiow.

The barrier consists of a metallic partition having holes through which current normally can flow without much hindrance. If the holes can be closed up or nearly closed by mechanical means, then current can be interrupted under -10 conditions where vapor pressure and current density are not too high. The barrier is analogous to a grid wherein the openings can be made "small. It is well known that current cannot ,spot through a grid if the openings are smaller than some definite value depending upon current density. The higher the current density, the smaller the openings must be to prevent spotting through.

m The barrier to be described is more, however,

current at the desired interval and not to hinder but even assist conduction at the interval when conduction is desired.

The device shown in Figs. 1 and 2 comprises a sealed envelope I, of any suitable material, such as glass, containing a cathode 2 and two anodes 3. The cathode 2 is mounted on a stem 5 while the two anodes 3 are mounted on stems 8 in the side arms 1 formed as part of the envelope I. The envelope I is filled with an ionizable atmosphere, such as mercury vapor, supplied from a body of mercury 4. Other situable vapors or gases, or mixtures thereof, can be used. The cathode 2 consists of a filament which is adapted to be heated to temperature of copious thermionic emission. It may be supplied with heating current from any suitable source, such as, for example, a transformer 3| whose primary 32 is connected to a source of alternating current, and whose secondary 30 is connected to the terminals of the filamentary cathode 2. Upon heating of the cathode, a discharge will flow between the cathode and the anodes under the proper conditions.

In order to interrupt the flow of current between the cathode 2 and the anodes 3, there is provided a barrier mechanism comprising a metal cylinder 8 inside of which is rotatably supported a shutter member 9 in the form of a metal cylinder. The cylinder 8 is supported from a stem 18 by means of metal standards II. A plurality of spring members 8 are mounted on the outer wall of the cylinder 8. These spring members contact the side walls of the envelope I and thereby resiliently center the cylinder 8 in the envelope I, and also aid in the support of said cylinder. The cylinder 8 is provided with a closed top in which is carried an insulating bushing l2 in which a shaft l3 carrying the shutter member 9 rotates. The shutter 9 is also provided with a closed top through which the shaft I3 passes, and which is securely fastened to' said shaft IS. The shutter 9 is open at the bottom where it carries a spider i8 which is also secured to the shaft 13. The upper end of the shaft I3 is mounted in a bearing [4 carried by a spider l5 which is mounted on the standards II. The bearing I4 insulates the shaft l3 from the spider l5, as indicated diagrammatically by the cross-hatching in Fig. 1. The lower end of the cylinder 8 is also open where it carries a spider II on, which is mounted a bearing IS. The lower end of'the shaft I3 is received in the bearing l6 which insulates the shaft I3 from the spider I1, as indicated diagrammatically by the cross-hatching in Fig. 1. In this way the shutter 9 is free to rotate within the cylinder 8, but is electrically insulated therefrom.

The cylinder 8 is provided with an opening I9 adjacent the entrance to each side arm 1. The shutter 9 is provided in its side wall with a plurality of openings 28. Although any number of such openings may be provided, three are shown in the embodiment illustrated. The openings 20 are located so that as the shutter 9 rotates, the openings l9 and '29 are periodically brought into alignment. Since both the cylinder 8 and the shutter 9 are open at the bottom, a gaseous discharge path is provided from the cathode 2 to each anode 3 as the openings l9 and 20 are brought into alignment with said anode.

The spacing between the side walls of the cylinder 8 and the shutter 9 is made as small as practical, for example, about one millimeter. A positive ion sheath which exists between a positively and a negatively-charged electrode is one in which substantially no electrons exist and in which exist a large number of positive ions. Thus if an electron passes into such a positive ion sheath, it is quickly swept out toward the positive electrode. If the distance between the electrodes is less than the thickness of the sheath, the electron is immediately captured by the positively-charged electrode before it can pass any substantial distance transversely to the juxtaposed surfaces of these electrodes. For this reason, I believe that if this distance is smaller than that of any positive ion sheath which may likely be formed, a discharge cannot pass through the space between the members 8 and 9. The spacing between the walls of the envelope I and the member 8 is also of the same order. I prefer to operate my device at relatively low vapor pressures and at relatively low current densities through the openings l9 and 20. For example, the vapor pressure may be between one micron and ten microns, and the current density below about ten amperes per square centimeter. Higher values of pressure up to about I08 microns and higher current density may be used under proper conditions.

With the spacing between the members 8 and 9 as described, a discharge can pass to the anodes 3 only when the corresponding openings i9 and 28 are in alignment. As the shutter 9 rotates and the size of the opening to the anode is thus decreased, the discharge will be cut ofi when the size of said opening approaches that of the spacing between the members 8 and 9. The openings 20 in the shutter 9 are arranged so that a discharge is permitted to flow alternately to the two anodes 3, as shown most clearly in Fig. 2.

In order to produce the rotation of the shutter 9, a rotor member 2| is mounted upon the shaft l3. The rotor member is made of magnetic material and provided with a plurality of uniformly spaced salient poles. A pair of external pole pieces is disposed adjacent the rotor member 2|. These pole pieces 22 are energized by alternating current from a transformer 23 connected to a suitable source of alternating or pulsating current. Thecombination of the rotor member 2| and the pole piece 22 constitutes a synchronous an auxiliary anode 24 is supported on the stem 8 adjacent the cathode 2. An auxiliary discharge is maintained between the cathode 2 and the auxiliary anode 24 by connecting a suitable source of potential, such as a battery 25, between them. A conductor 28 leads from the anode 24 through a current-limiting resistor 21 to a conductor 28 which is connected to the positive terminal of the battery 25. A conductor 29 connects the negative terminal of the battery 25 to the midpoint of the secondary 38 of the cathode-heating transformer 3|. Thus the battery 25 causes a current to flow between the cathode 2 and the auxiliary anode 24 which produces the desired supply of positive ions adjacent the cathode.

Under the conditions which I have specified, I have found that it is also desirable to devise some means for providing a steady supply of positive ions adjacent the openings 28 so as to insure uniform starting of the discharge through these openings. In order to do this a small discharge is maintained between the cathode 2 and the shutter 9, by connecting suitable source of potential, such as the battery 25, between them. A brush 33 supported by the insulating bearing I4 makes contact with the shaft l3, and by means of a conductor 34, which is sealed in the stem I0, is connected through a current-limiting resistor 35 to the conductor 28. As pointed out above, the conductor 28 is connected to the positive terminal of the battery 25, while the negative terminal thereof is connected by means of the conductor 24 to the cathode 2. The battery 25 so connected causes a'small current to flow between the cathode 2 and the shutter 9 which maintains the desired supply of positive ions adjacent the openings 28. In some instances the auxiliary anode 24 may be omitted, in which case the discharge to the shutter 9 supplies the positive ions adjacent the cathode.

It is also desirable to apply a negative potential to the cylinder 8. This negative potential sets up a field in the space between the members 8 and 9, and also between the member 8 and the walls of the envelope I, which deflects any electrons which enter these spaces. For this purpose a conductor 36 leads from one of the standards I to the negative terminal of a biasing battery 31. The positive terminal of the battery 31 is connected by means of a conductor 38 to the midpoint of the secondary 38. The application of a negative potential to the cylinder 8 makes the positive ion sheath which forms adjacent its surface thicker than if such a potential were not applied. Thus, with such a potential, the spacing between the members 8 and 9 can be increased over what would be necessary in absence of such a field. The negative potential so applied tends to prevent a discharge between the cylinder 8 and the shutter 9 and also aids in the shutting off of the discharge as the openings i9 are closed by the shutter 9. By controlling the potential applied by the battery 31, the exact time of the starting and stopping of the discharge through the opening IS with respect to the position of the shutter 9 can be controlled.

A suitable source of potential may be impressed between the cathode 2 and the anodes 3 in order to produce the discharge which is controlled as described above. In Fig. l the battery 25 supplies this potential. Conductors 39 and 40 lead from the two anodes 6 to the opposite sides of the primary 4| of an output transformer 42 having a secondary 43 connected to any suitable output device. A conductor 44 leads from the center of the secondary 43 to the positive terminal of the battery 25. The negative terminal of the battery, as pointed out above, is connected to the cathode 2.

When the device 'is connected as described in connection with Fig. 1, the shutter 9 will be set in rotation, and the various discharges will pass as described above.' Thus a current will flow alternately in the circuits of the two anodes 3 which will set up current pulsations in the primary winding 42, whereupon an alternating output voltage will appear across the secondary winding 43 and an alternating load current will be fed to the output device. The frequency of the alternating current output will be determined .:y the speedof rotation of the shutter 9 and also by the number of openings 28 therein.

The embodiment shown in Figs. 3 and 4 comprises a sealed envelope 44 containing a cathode 45 and two anodes 46. The cathode 45 is mounted on a stem 41 at one end of the envelope 44, and the anodes 46 are mounted on a stem 48 at the other end of the envelope. In order to increase the permissible voltage which can be applied between the anodes, glass sleeves 49 may be formed on the stem 48 around the supporting standards 58 of the anodes 46. As in the case of Fig. l, the envelope may be filled with mercury vapor from a body of mercury 52 or with other gases or vapors. The cathode 45 may consist of a filament which is adapted to be heated to temperature of thermionic emission by heater current supplied from a heating transformer 53. The secondary 54 of the transformer 53 is connected to the terminals of the cathode 45, and the primary 55 of said transformer is connected to some suitable source of alternating current.

The barrier for interrupting the flow of current between the cathode 45 and the anodes 46 comprises a metallic barrier 56. The barrier 56 has a cylindrical wall 51 which is approximately the same size as the inside diameter of the envelope 44, and is supported therein by means of indentations 58 formed in the wall of the envelope 44, and which project over the upper and lower edges of the wall 51. The wall 51 carries a lower partition 59 which extends across the member 51 and blocks off the gaseous discharge path therethrough, except at openings 68 which are provided in the partition 59 opposite each anode 46. The wall 51 also carries an upper partition 6| similar to the lower partition 59, and likewise provided with openings 62 opposite each anode 46 and in line with the openings 68.

A shutter 63 is rotatably supported between the upper and lower partitions. The shutter 63 may be made of a solid piece of metal, although in order to cut down on the weight thereof, I prefer to have it hollow, as shown in Fig. 3. The shutter 63 is mounted on a shaft 64 which extends into tubular extensions 65 and 66 formed in the upper and lower partitions, respectively. The outer end of the tubular extension 66 is closed by an insulating block 61 which carries a bearing 68 in its upper face. The lower end of the shaft 64 is received in the bearing 68. In this way the shutter 63 is shielded from a discharge to the cathode 45, except through the openings 68. The upper end of the tubular extension 65 is closed by an insulating block 69 which carries a combined bearing and contact 18. The upper end of the shaft 64 is received in the bearing 18. Due to the support arrangement described, the shutter 63 can rotate between the partitions 59 and 6|, and is electrically insulated therefrom.

In order to permit current to now at predetermined intervals to the anodes 46, the shutter 83 is provided with a series of openings I! preferably spaced at regular intervals. Three such openings may be provided, as shown in Fig. 4.

The wall 51 preferably is also provided with an anode-shielding member 12 which extends entirely across the inside of the wall member 51, and is provided with an opening for each of the anodes 46. A tubular extension 13 is provided around each opening and surrounding each anode. These tubular extensions reach from the member 12 to the upper partition 6|, as shown. Due to this shielding arrangement, the discharge which passes to the anodes is confined to the ends of the anodes, and electrons and positive ions from the discharge cannot pass up into the space between the anodm or their supporting standards. In this way a higher voltage may be impressed between the anodes without danger of a breakdown discharge occurring between them.

The spacing between the partitions 59 and 6] and the shutter 63, and also between the anodes 46 and the members 13 is preferably of the order of magnitude as described in Fig. 1 in connection with the spacing between the members 8 and 9. The pressure and current density are also preferably of the orderof magnitude as described in connection with Fig. 1.

Rotation is imparted to the shutter 63 by disposing coils 14 around the envelope 44 to set up a magnetic field parallel to the axis of the envelope 44 and also at right angles to the plane of the shutter 63. The coils 14 are energized from any suitable source of current, such as a battery 15. A conductor 16 extendsfrom one terminal of the battery to the coils 14 which are connected in series. Another conductor 11 leads to an adjustable resistance 18 from which a conductor 19 completes the circuit to the other terminal of the battery 16. Current is caused to flow in the shutter 63 to produce a reaction upon the field of the coils 14 in order to impart rotation to said shutter. For this purpose a conductor 88 is connected to the bearing contact 18, passes through the stem 48, and extends to an adjustable resistance .3l. Conductors 82 and 83 extend the circuit to the positive terminal of a source of direct current which in Fig. 3 is shown as the battery 15. The negative terminal of the battery 15 is connected by means of a conductor 84 to a center top in the secondary 54 of the cathode-heating transformer 53. .In this way a potential is applied between the cathode 45 and the shutter 63, tending to cause a current to flow between the cathode and the shutter 63. The only way in which such a discharge can reach the'shutter 63 is through the openings 68 in the lower partition 59. The only way in which current can flow to the shutter 63 from the positive terminal of the battery 15 is through the shaft 64 which is connected to the shutter at its center. Thus when the discharge current flows between the cathode 45 and the shutter 63, a current will flow from the central shaft 64 radially through the shutter 63 toward the openings 68. The direction of this current flow is at right angles to the direction of the flux of the coils 14. The combination of the coils 14 and the shutter 63 forms in eflfect a unipolar motor, and thus a turning force is imparted to the shutter 63 which is thereby continuously rotated. The speed of rotation can be controlled by controlling the strength of the field by means of the resistance 18 or the strength of the current in the shutter 83 by means of the resistance 8|, or both.

In order to produce a continuous supply of positive ions adjacent the openings 88, a potential is also preferably connected between the barrier 56 and the cathode 45. For this purpose a conductor 85 is connected to the wall member 51, passes through the stem 41, and extends to a current-limiting resistor 86. The circuit is then extended to the positive terminal of the battery I5 by the conductors 82 and 83. The negative terminal of the battery 15 is connected to the cathode 45, as pointed out above. Thus a small ionizing current is caused to flow between the cathode and the barrier 56, supplying-the ions desired adjacent the openings 60. It will be noted that an auxiliary anode, such as 24 in Fig. 1, is missing, the function of such an auxiliary anode being supplied in this case by the barrier 56 acting as an anode.

A suitable source of potential is impressed between the cathode 45 and the anodes 46 in order to produce the discharge which is controlled as described above. In Fig. 3 the common battery 15 is used to supply this potential. Conductors 81 extend from the two anode standards to opposite sides of the primary winding 88 of an output transformer 89 whose secondary winding may be connected to a suitable output device. A conductor 8| connects the midpoint of the primary 88 to the positive terminal of the battery 15. The negative terminal of the battery, as pointed out above, is connected to the cathode 45.

It will be noted that the field set up by the coils I4 is parallel to the axis of the openings 68, 82 and 1|. Thus when the discharge tends to flow through said openings when they are aligned, the focusing efiect of the field will assist the discharge in passing through the openings. However, if as the openings 1| pass out of alignment with the openings and 82, and the discharge tries to continue to flow, the path of said discharge would necessarily have to be bent so that it cuts the flux lines of the coils 14. The field in such a case would lead the electrons into the surfaces of 83 or 6!, facilitating recombination of ions and electrons and thereby tending to prevent such a discharge from passing, and thus insures a definite cutting off of the discharge as the shutter 63 rotates. To the extent that the field tends to prevent the discharge from passing in the space between the shutter 63 and the partitions, this field assumes the function of the negative potential applied to the member 8 in Fig. 1. When the device is connected as shown, the shutter 83 will be set in rotation, and as the openings H are brought into alignment with the openings 60 and 62, current will flow alt... mtely to the two anodes 46. Thus current pulsations will fiow alternately in the two halves of the primary winding 88 which in turn will produce an alternating voltage across the secondary winding 98, whereby the output device may be supplied with alternating current. The frequency of the output is controlled by the speed of the shutter 63 ,and the number of openings ll.

This invention is not limited to the particular details of construction or operation, as de scribed above, as many equivalents will suggest themselves to those skilled in the art. For example, instead of using two anodes as shown, any number of anodes can be used, and also plural phase instead of single phase current produced. The number of openings in the shutter can be any convenient number. The cathode need not be a filament but can be of any convenient form. Instead of the current being symmetrical to the anodes, for some purposes it may be asymmetric, as, for example, by locating the openings adjacent the anodes at difierent places with'respect to the anodes, or by changing the size of the openings. Also instead of applying voltages to the elements of the barrier mechanism as indicated, varying values and polarity of such voltages may be utilized. In this way the time of the starting of the discharge can be controlled, and also the amount of current flowing to each anode. In this way the asymmetry mentioned above could be secured. Various other changes will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An electrical space discharge device comprising a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure sufiicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable shutter means adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, said barrier means and said shutter in the closed position having relatively extended juxtaposed surfaces spaced a relatively short distance apart and leaving a space into which electrons from said cathode have a tendency to pass, and means for setting up a field in said space for deflecting said electrons.

2. An electrical space discharge device comprising a cathode, an anode, metallic barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure suflicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable metallic shutter means adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, said barrier means and said shutter in the closed position having relatively extended juxtaposed surfaces spaced a relatively short distance apart and leaving a space into which electrons from said cathode have a tendency to pass, said barrier means and said shutter means being insulated from each other, and means for applying a negative potential to one of said means, whereby a field is set up in said space for deflecting said electrons.

3. An electrical space discharge device comprising an envelope containing a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure sufiicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable shutter means adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, said barrier means and said shutter in the closed position having relatively extended juxtaposed surfaces spaced a relatively short distance apart and leaving a space into which electrons from said cathode have a tendency to pass, said barrier also being spaced a short distance from the walls of said envelope leaving a space into which electrons from said cathode tend to pass, and means for setting up a field in said spaces for deflecting said electrons.

4. An electrical space discharge device qomprising a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure suiiicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable shutter means adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, said barrier means and said shutter means in the closed position having relatively extended juxtaposed surfaces spaced a relatively short distance apart and leaving a space into which electrons from said cathode have a tendency to pass, and means for setting up a magnetic field in said space for deflecting said electrons to prevent them from building up a discharge through said space.

5. An electrical space discharge device comprising a cathode, an anode, metallic barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure suflicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable metallic shutter means adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, said barrier means and said shutter in the closed position having relatively extended juxtaposed surfaces spaced a relatively short distance apart and leaving a space into which electrons from said cathode have a tendency to pass, said barrier means and said shutter means being insulated from each other, means for applying a positive potential to one'of said means for producing a discharge from said cathode, whereby a supply of positive ions is available adjacent said opening whenever the opening is uncovered by said shutter, and means for applying a negative potential to the other '01 said means, whereby a field is set up in said space for deflecting said electrons.

6. An electrical space discharge device comprising a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure suillcient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable shutter means adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, and means tor applying a positive potential to one of said means for producing a discharge from said cathode, whereby a supply of positive ions is available adjacent said opening whenever the opening is uncovered by said shutter. 7. An electrical space discl rge device comprising a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure suiiicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and a disc-shaped metallic shutter rotatable in the plane of said disc and adapted to periodically open and close said opening to the passage of a discharge between said cathode and anode, means for causing a current to flow radially in said disc, and means for setting up a magnetic field having a component at right.

angles to the plane of said disc, whereby said disc is driven as a unipolar motor.

8. An electrical space discharge device comprising a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure sufiicient to neutralize space charge upon the passage of a discharge therein, and a disc-shaped metallic shutter rotatable in the plane of said disc, said shutter being adapted to support a discharge in said atmosphere between a localized portion of said shutter and one of the other electrodes, means for establishing an external electrical connection to said shutter at another portion spaced radially from said localized portion, whereby a current flows radially in said disc, and means for setting up a magnetic field having a component at right angles to the plane of said disc, whereby said disc is driven as a unipolar motor.

9. An electrical space discharge device comprising a cathode, an anode, barrier means interposed between said cathode and anode, said discharge device containing an ionizable atmosphere at a pressure suflicient to neutralize space charge upon the passage of a discharge therein, said barrier means having an opening through which a discharge may pass between said cathode and anode, and movable shutter means adapted to periodically open and close said opening to the passage 01' a discharge between said cathode and anode, said barrier means and said shutter in the CHARLES G. SMITH, 

